This invention is related to an apparatus for detecting an enemy's infrared camera.
We know that such a camera includes a periodical line scanning system of the infrared energy situated in a particular sector of space, a convergent optical system capable of concentrating the infrared energy scanned by the scanning system, an infrared electronic detector placed in such a way that it can receive the energy concentrated by the optical system, and a visualising system connected to the scanning system and to the electrical output of the detector to form the thermal picture of the sector, on a screen.
An apparatus to detect such a camera has been proposed, which includes:
a laser generating an infrared beam, PA1 an orientable reflector to direct the infrared beam to the camera, the optical system of the camera then sending infrared signals to the reflector, PA1 an infrared electro-optical receiver positioned to receive the said infrared signals reflected by the reflector, the receiver including a first and a second electrical output, the receiver supplying on its first output, reception electrical signals showing the intensity of the infrared signals and supplying on its second output, vertical reference electrical signals showing the discrepancy between a reference point on the sensitive area of the receiver and the receiving points on this surface of the infrared signals, PA1 a servo-control system connected to the second electrical output of the receiver which receives the vertical reference electrical signals, this system being able to control the positioning of the reflector so as to reduce the said discrepancy, PA1 an electro-optical range-finder, PA1 and means to position the range-finder towards the camera, these means being connected to the reflector positioning servo-control system, the range-finder being able to indicate periodically the distance from the camera, PA1 a processing circuit connected to the range-finder to receive the indication of the camera distance and connected to the first electrical output of the receiver to measure the time intervals between the reception electrical signals, in order to determine the line rate and the picture rate of the camera scanning system, this processing circuit being able to determine a delay time on the basis of the camera distance and these rates, PA1 a delay circuit, connected to the processing circuit to supply, at the same speed as the picture rate, a control electrical signal delayed by the said delay time in relation to the reception signal, PA1 and means to emit a laser pulse towards the reflector, in parallel with the emitting axis of the laser generator, these means being connected to the delay circuit so that a pulse is emitted each time a control electrical signal is emitted, this laser pulse being reflected towards the camera by the reflector and appearing on the camera screen as a second very bright spot, the delay time determined by the processing circuit being higher than a minimum value and lower than a maximum value, the minimum value being determined so that the second spot represents a picture of a dummy object which is further away from the apparatus than a pre-set distance, the maximum value being determined so that the second spot creates a dazzling effect on the screen, this dazzling being strong enough so that the first spot is no longer visible.
a first spot being formed on the screen of the camera every time the scanning system directs to the detector the energy of the infrared laser beam concentrated by the optical system, the latter sending back to the apparatus, by catadioptric effect, an infrared signal constituted by part of this concentrated energy, the receiver supplying in return a reception electrical signal on its first electrical ouput.
However, the proposed apparatus cannot be used in practice because the enemy can immediately spot the detection apparatus thanks to the spots formed on the screen of his camera, and it is then easy for him to aim a weapon in the direction of the detection apparatus.